Alex Cornell created an example of the "Worst Portfolio Ever" with design mistakes many people do with their portfolio sites. Here are the mistakes:
1. Intro text is unnecessary and too long.
2. Too many social media links that lead away from your site. You want to showcase your work, not your online presence.
3. Arbitrary skills chart that don't make sense. It is better to clearly state your proficiency instead of using percentages
4. Pictures that don't show your work are distracting and have no purpose if they are not related to the work you do